Abstract: Underground coal gasification (UCG) is of great strategic significance for optimizing China's energy structure. To elucidate the influence mechanism of gasifying agent parameters on product composition, response surface methodology (RSM) was integrated with process simulation to systematically investigate the synergistic effects of key parameters—including oxygen and water flow rates, temperature, and pressure of the gasifying agents—on the main components of syngas (CO, CO₂, H₂, and CH₄).A UCG process simulation model was established using Aspen Plus software. The Plackett−Burman method was adopted to design parameter combinations, and significant influencing factors were screened based on simulation results. Steepest ascent experiments were conducted to approach the optimal parameter region, and second−order response models were developed via central composite design (CCD). The results show that oxygen flow rate, water flow rate, and water temperature exhibit dominant effects on product composition, with significant interaction effects observed. The conditions for maximizing CO and H₂ contents while minimizing CO₂ content are characterized by an oxygen flow rate approaching the maximum value and an oxygen−to−water ratio close to 1:1. For maximizing CH₄ content, the optimal conditions involve an oxygen flow rate near the minimum value and an oxygen−to−water ratio approaching 1:4, whereas higher water temperatures are favorable for promoting the reaction. Based on the CCD results, second−order equations correlating product compositions with influencing factors were regressed, with the coefficient of determination (R²) approaching 1. Further model validation demonstrates a high agreement between predicted and simulated values, confirming the reliability of the proposed method. The findings provide important theoretical support for the optimization of UCG processes.